A tubular bag made of airtight flexible material which is hermetically sealed and folded so as to produce a package of substantially parallelepipedic shape is customarily used for the vacuum packaging of various products, especially ground or granular coffee. In most cases, the bag constitutes in practice an inner envelope coming directly into contact with the packaged product and is covered with an outer envelope folded so as to have the same parallelepipedic shape as the bag constituting the inner envelope.
In order to open the packet composed of the two envelopes in this way, it is necessary to lift the two triangular flaps forming the upper end face of the packet, separating them from one another so as to release the upper end zone of the bag. This end zone is composed of two rectangular surfaces projecting upwards from the upper face of the bag and the long sides of which are respectively the end edges of the opposite faces of the bag and fold lines at the level of the upper face of the bag, the bag being sealed in this rectangular zone by a linear region or weld line which extends parallel to the long sides of the rectangular zone, in general substantially midway between them.
In order to open the bag, it is necessary to break the weld line in the rectangular zone. In view of the mechanical characteristics of the material, such as a plastic film/aluminum foil composite, constituting the bag, this tearing is performed with difficulty and above all in a manner which is not reproducible from one bag to another, as a result of which the users, not being able to open the packet simply by tearing, in practice use cutting means such as scissors to open the bag.